Modular furniture units such as for example wall panels are widely used in architectural design, especially for commercial establishments, because of the advantages they provide in ease of installation, convenience of rearrangement of floor plans after installation, attractiveness of appearance, etc. One problem encountered in the use of modular wall panels is the provision of adequate electrical power for the areas enclosed by the panels while still retaining the advantage of flexibility in the location of the panels. This problem has been answered to some extent in prior power distribution systems disclosed, for example, in U.S. Pat. No. 4,060,294, issued Nov. 29, 1977 and related U.S. Pat. Nos. 4,370,008, issued Jan. 25, 1983 and 4,199,206, issued Apr. 22, 1980.
In the system of the above-referenced patents, identical power blocks are secured within the bottom edge of each panel unit adjacent the opposite ends thereof. The power blocks are interconnected by three conductors running the length of the panel within the bottom edge and are adapted to receive, on either of their opposite vertical faces, panel to panel jumper connectors or a power-in connector through which power is supplied by a three conductor cable from a branch circuit of the base power distribution system. The power blocks are further adapted to receive, on either vertical face, a duplex outlet connector through which outlet power is available to the areas enclosed by the panels. By these means, a duplex outlet may be provided at each of the opposite ends of a panel unit, and on both sides thereof, along the length of an indefinite run of panel units, limited by the permissible number of outlets that can be connected to a single branch circuit. When the number of outlets installed along a panel run has reached the permissible limit, it is necessary to break the continuity of the system and to begin a new run from a separate power-in connector leading from a different branch circuit of the power main.
Improvements over the three-wire power distribution system for modular panels have been devised to enable the installation of longer panel runs and the placement of a greater number of duplex outlets therein with fewer power-in connections from separate branch lines of the base power distribution system. Such improved systems are exemplified by the systems disclosed in U.S. Pat. Nos. 4,313,646, issued Feb. 2, 1982; 4,367,370, issued Jan. 4, 1983; and 4,740,167, issued Apr. 26, 1988. The systems of U.S. Pat. Nos. 4,367,370 and 4,740,167 employ power blocks at opposite ends of a panel unit which are adapted to receive connectors for panel to panel jumper cables, connectors for cables interconnecting the power blocks of a panel unit and for power-in cables, and duplex outlet connectors on the opposite vertical faces. In the system of U.S. Pat. No. 4,313,646, the power blocks are formed integrally with a single duplex outlet.
The feature in common of the '646, '370 and '167 patents is that each of the systems is supplied power through, and the power blocks are interconnected by, a five-wire cable. The base power distribution system may suitably comprise a three phase system and the five wires provide three lines, one shared neutral and one safety ground. The duplex outlets may be selectively connected between any one of the three available lines and neutral. The five-wire panel distribution systems enable the installation of panel runs having more than one circuit within a panel.
To overcome the limitation imposed by the load capacity of a shared neutral conductor, U.S. Pat. No. 4,781,609 issued Nov. 1, 1988, discloses a seven-wire power distribution system for modular panels providing three lines, three neutrals, one for each of the available lines, and one safety ground.
Increasing the number of conductors in a power distribution system for a panel originally designed to accommodate a three-wire power distribution system presents a challenge as to the manner in which the additional number of conductors are to be fitted into the available space. In the system of U.S. Pat. No. 4,781,609, the power blocks contain seven vertically aligned, parallel conductive plates. Each of the plates is formed with prongs projecting outwardly from both sides near one end of the plate and with two prongs spaced along the length of the plate projecting outwardly from opposite sides of the plate. Each of the projecting prongs is surrounded by an insulating shroud to protect against accidental contact. The vertical spacing between the plates is necessarily increased to provide space for the horizontal walls separating the vertically aligned insulating shrouds, so that the height of the power block extends substantially the entire available height of the wiring channel in the lower edge of the panel. Also, the outwardly projecting prongs and insulating shrouds increases the thickness of the power blocks, necessitating a reduction in the thickness of the duplex outlets used with the power blocks, if the faces of the duplex outlet units are to be maintained flush with the bottom edge of the panel unit.
The present invention comprises a ten-wire power distribution system for modular furniture units such as for example wall panels. The system provides four lines, four separate neutrals and two separate grounds, one of which comprises a safety ground for use by the outlet units of the system and the other of which comprises an isolated ground for use in specialized circuits.
It is an object of the invention to provide a ten-wire power distribution system for modular wall panel units which enables the installation of outlets at both ends of the lower edge of a panel unit, and on both sides thereof, with the four outlets being connected, at the choice of the user, (a) to separate pairs of line and neutral conductors, or (b) to the same pair of line and neutral conductors, or (c) to a pair of line and neutral conductors selectable from a combination of four separate pairs of line and neutral conductors.
It is another object of the invention to provide a ten-wire power distribution system for modular furniture units which is compact and space-saving in form to enable the system to fit within the space available in panel units of existing design.
It is another object of the invention to provide a power distribution system having provision for plug-in components in which the current carrying conductors thereof are at all times protected against accidental contact, including times during the insertion or removal of the plug-in components.